1. Field of the Invention
The invention relates to an internal combustion engine.
2. Description of Related Art
There is available an internal combustion engine that includes a first injection unit that injects fuel into an intake passage communicating with a combustion chamber and a second injection unit that injects fuel into the combustion chamber (see, for example, Japanese Patent Application Publication No. 2007-127059 (JP 2007-127059 A). Other techniques that can be considered to be relating to the invention are disclosed, for example, in Japanese Patent Application Publication No. 2010-265814 (JP 2010-265814 A), Japanese Patent Application Publication No. 2008-57380 (JP 2008-57380 A), Japanese Patent Application Publication No. 2005-201083 (JP 2005-201083 A), and Japanese Patent Application Publication No. JP 2011-241714 (JP 2011-241714 A).
JP 2010-265814 A discloses the technique for promoting the atomization of the fuel injected form a port injection injector by the blowback of gas into an intake port. JP 2008-57380 A discloses the technique for injecting fuel in an exhaust stroke when the engine is started. JP 2005-201083 A discloses the technique for removing the deposit building up in the nozzle of a cylinder injection valve by performing fuel injection only with the cylinder injection valve for a predetermined period even in an operation region in which fuel injection is performed by an intake passage injection valve. JP 2011-241714 A discloses the technique for injecting a small amount of fuel from a cylinder injection valve within a minus overlap period and injecting fuel for output control from a port injection valve in the intake stroke.
In the internal combustion engine including the first and second injection units, the required injection amount is sometimes less than the sum total of the lowest injection amounts that can be injected by the injection valves. In such cases, where an attempt is made to inject fuel from both injection units, the amount of the supplied fuel becomes larger than the required injection amount and the fuel-air mixture becomes rich, thereby destabilizing the combustion. To resolve this problem, the required injection amount can be injected, for example, from the first injection unit, from among the first and second injection units. As a result, the fuel is supplied under a low pressure and the injection amount is easily controlled, thereby making it possible to obtain stable combustion.
However, in such cases, the fuel is not injected from the second injection unit. Therefore, in such cases, deposits can appear and build up in the nozzle of the second injection unit. Meanwhile, in order to clean the exhaust gas in the internal combustion engine, it is desirable that warm-up of a catalyst be promoted in the case in which the bed temperature of the catalyst is lower than a predetermined temperature (for example, activity temperature).